The existing wafer inspection tools have marginal illumination capabilities due to naturally low brightness of arc lamps. High-powered lasers are often used as a source of illumination in lithographic systems. In general, suitable high-powered lasers are available in infra-red and visible light range. Generation of a UV (ultra-violet) or DUV (deep ultra-violet) illumination is obtained by third or fourth harmonic generation. The harmonic generation involves non-linear optic that is effective only at very high light intensities. Such high intensity can be achieved either by placing non-linear optic inside a high-quality resonator or by the use of pulse lasers. Short pulse lasers, such as mode-locked lasers, are often used because they are relatively inexpensive. The pulse lasers generate relatively short high intensity pulses. The short pulse DUV illumination, over time, damages optical components. The laser induced damage strongly depends on peak power of the illumination light.
It is within this context that embodiments of the present invention arise.